1. Field of the Invention
The present invention relates generally to maritime navigational aids, and more particularly to a method and system for marine channel marking utilizing a single laser.
2. Description of the Prior Art
Marine channel marking for the purpose of navigation is currently accomplished by a variety of methods and systems. In the traditional system, buoys with flashing green or red lights mark the sides of the channel. The major shortcoming of this simple system is its inability to provide a ship's navigator with the proper bearing to steer through the channel. Rather, the navigator must pick his way through the channel as he visually encounters each buoy.
Another approach uses single station range lights which project a cone of light about a centerline of a marine channel. Different color light is visible from either side of the cone's centerline. The cone of light is further coded in such a way that the navigator can tell if he is near the centerline or the edge of the cone. Example of single station range light systems are disclosed in U.S. Pat. Nos. 3,354,428 and 3,781,786. However, the major shortcoming of these systems is that the navigator must actually be in the cone of light and be looking in the proper direction to use it as a navigation aid. Thus, this approach is only useful once the navigator is able to enter the channel in the first place, which may itself prove to be a difficult task.
Multiple color laser systems are currently being evaluated by the U.S. Coast Guard. Specifically, laser beams are projected above the water's surface to define the edges of a marine channel and/or its center. The use of different color lasers is being considered as a way of distinguishing one beam from another. However, the shortcomings of this approach include the need for several different types of lasers to produce the required colors and the fact that not all colors are equally visible to the human eye, especially against the variety of background lighting conditions normally experienced in coastal areas.